Othmab dbapal



Patented Sept. 13, 1932 o'rHMAn DRAPAL, F rRAnKronr-oN-rHn-nlnn,(:FERMANY, assro ron To enivnnArl ANILINE WORKS, 11m, or new YORK,1\T.Wj A oonronnrion or DELAWARE .IfMIEBOVING THE srABILIrY or pIAzosonn'rrons m rnnnrnnsnncn or raoiv I To Drawing. Application filedDecember 22, 1928, Seriai 1Y9, andin Germany December 192?.

In preparing the important ice-colors the dyer, when workingeconomically, is obliged to use apparatuses prepared from or containing.iron'and to dye in a standing diazo bath.

The standing bath requires a good stability of the diazo solutions,which stability. is much injured by the presence of iron. In this casethe diazo solutions are already entirely decomposed aftera short time,especially when containing an excess of an acid. Generally the diazocompounds, when in contact with iron in acid solution are inclined to aquick decomposition.

I have now found that the injurious in fluence of iron can be diminishedto a high degree by adding to the diazo solution agents capable ofconverting ferrous ions into ferric ones and which do not destroy thediazosolution. Nitrous acid is especial ,ly suitable for this purpose.My observation is all the more surprising as Schwalbe (Zeit' schriftfiir Farbenund Textil-Industrie, vol. 1905, No. 18) found that nitrousacid has a poisoning action on diazo compounds (page 485, line 10-11)and accelerates in a high degree, like a catalyst, the speed ofdecomposition (page 433, paragraph 2, line 114%) Therefore it was not tobe foreseen that the addition of nitrous acid would increase thestability of the diazo compounds. It might be rather assumed that theinjurious influenceof iron on the diazo compound would be raised by theaction of nitrous acid.

For technical purposes my process is ad-' ,vantageously carried out byadding nitrous acid to a diazo solution which will be employedin ironapparatus in an amount at least equivalent to the amount of alkali metalnitrite, for example, sodium nitrite, which was originally used to formthe diazo solution. The nitrous acid is preferably prepared by addingsodium nitrite to the corresponding amount of a free acid.

In order to illustrate the new process more fully the following examplesare given: Emample 1.1.'28 grs. of ortho-chloro aniline are dissolved in3 c. c. of hydrochloric acid of 20 B. and water; tothis solution 0.75grs. of sodium nitrite are added. When the diazo compound is formed, thesolution is I nearly neutralized with 6.85 grs. ofIsodium acetate andthe whole is made up to 1 liter.

A sq t e of. n t ous acid P a ed r 1 grfof sodium nitriteand a diluteformic acid is added to 500 c. c. of this diazo solution, the other 500c. 0. remains without any addi- Example Q.A solution of the diazoniumchloride of the amino azo body prepared from para-nitraniline and aminohydroquinone dimethyl ether, which solution contains 0.925 grs. of thebase per liter and to which 1.1 grs. of crystallized aluminium sulfatehave been added, is divided into 2 equal parts, one part being mixedwith a solution of nitrous acid porresponding to 2 grs. of sodiumnitrite per iter.

Both solutions are subjected at about 18 C. while stirring to the sameaction of iron and after 1, 2 and 3 hours the degree of decom positionof each is determined by examining the content of the solutions.

tion. Then both solutions are exposed to the The following table showsthe degree of decomposition in both solutions:

The aforesaid numbers explain the favorable influence of nitrous acid onthe stag 2 Lea-6,8525

iron.

I claim: V v 1. A method of improving the stability of 5" a .diazosolution in the presence of iron which comprisesadding nitrousacid tosaid di'azo "solution in an amount at least" equivalent to the amount ofalkali metal nitrite" original bility of diazo compounds in the presenceof ly used to form'thediazo solution.fl .1 if; H;

.10 2. A-methodofimproving thestability ofv j a V a diazo solution inthe presence of iron which oomprises adding'a solution of an alkalimetal I? I nitrite in a corresponding amountof a free 7 acid to "said'di'aZosolutionthe amount of 15 alkali metal-nitrite thus added. beingat least equivalent to the amount of alkali metal ill-'- triteoriginally used to form the diazo solution. I I

In testimony whereof, I afiix mysignature.

-50 OTHMAR D PALH a

